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Re: Re: Allow Reg Expressions in Position function - Mailing list pgsql-general

From Geoff Winkless
Subject Re: Re: Allow Reg Expressions in Position function
Date
Msg-id CAEzk6fdJwwG9aOFBDy-Vkj7OLZwvDriBvLU7Omuw0XEebbdtqw@mail.gmail.com
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On Mon, 20 Aug 2018 at 09:22, Nick Dro <postgresql@walla.co.il> wrote:

This incorrect.
SELECT position(substring('https://www.webexample.com/s/help?' FROM '/(s|b|t)/') IN 'https://www.webexample.com/s/help?');
 
Gives 5. It's wrong.



On Mon, 20 Aug 2018 at 09:22, Nick Dro <postgresql@walla.co.il> wrote:

This incorrect.
SELECT position(substring('https://www.webexample.com/s/help?' FROM '/(s|b|t)/') IN 'https://www.webexample.com/s/help?');
 
Gives 5. It's wrong.

For some reason, substring() returns the parenthesised subexpression rather than the top level.

The comment in testregexsubstr does say that it does this, but it's not clear from the documentation at all, unless I'm missing where it says it.

You can work around this by putting parentheses around the whole expression, because that way the first subexpression is the whole match.

db=# SELECT position(substring('https://www.webexample.com/s/help?' FROM '(/(s|b|t)/)') IN 'https://www.webexample.com/s/help?');
 position
----------
       27

Geoff

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